Picture telegraphy



@CL l2, 1937. HERRMANN PICTURE TELEGRAPHY' Filed July l2, 1932 f INVENTOR JWN/IE5 HERMA/VA BY #QQ ATTORNEY Parenteel oet. 12, 1937 A wir PATENT sie PICTURE TELEGRAPHY Johannes Herrmann, Berlin-Siemensstadt, Germany, assignor to Siemens & Halske, Aktiengesellschaft, Siemensstadtrinear Berlin, Gier,-` many, a corporation of Germany Application July 12, 1932, Serial Nei 622,045

In Germany July 13, 1931 6 Claims.

The invention isconcerned with improvements upon a method used-for picture-telegraphy in which the various shadings or densities' of a picture are converted intoinormal telegraphic 'signals orimpulses, the constituent shading values being recorded upon perforated tapes customary in telegraphic apparatus in such a way that the number or position of the holes of a transverse row' of the tape results in the shade or brightness of a picture unit or point. For each scannedv picture unit across-row on the tape and thus, in thei'transmission of thepicture, production Vof an impulse for each picture point is required. A l Thesaid perforated strip is then passed through I54 a telegraph transmitter and may be transmitted through any desired telegraphing channel. the receiving station the incoming perforated strip serves directly for the control of a pencil of light whereby the transmitted picture is recreated photographically.`

Methods are known in the prior art in which the carrier wave modulated by the picture currents, after rectification, are fedthrough a commutator in denite sequence to a number of polarized relays which in accordance to the Various shadings are adjusted to different intensities of current. These relays operate the corresponding perforator magnets.

f Arrangements of this kind involve the disadvantage that they require .a good deal of equipment in the line of sensitive relays and they require a photo cell amplifier insuring a large output power inasmuch as the entire energy required for the actuation of the equipment must be supplied by this amplier. Hence, the photo cell currents influence' directly all` of the relays of themeans used to produce the perforated paper strip; e

The invention obviates these 4drawbacks by 402 utilizingthe ampliiied photo cell currents only Inediately for the conversion of Vshade values of apicture into telegraphic impulses. The subdivision of the shading according to a dual systemjpowers of two) makes it possible at the same time vto getalong with a minimum number offrelays.- ,-1,

The photo cell currents in a compensating circuit scheme servegpnly mediately for the control of the conversion relays, the energy required by the latter being furnished from a local source of current. The power demanded of the photo cell amplifier as a result is decreased to not more than one-tenth of the energy so far required.

The photo-electric current modulated by the4 shading values or densities of the picture, in a bridge arrangement, is compared with a nonmodulated photo-'electric current adjusted in accordance with the desired number of shading Values and being, for instance,` variable by stages. The standard circuit contains a series connec- `5 tion ofresistances graduated according to dual numbers. The said resistance is cut in circuit or short-circuited by the agency of a polarized relay included in a local circuit and keyed by a cam Contact disk. Accordingk to whether the 10 modulated current is larger lorsmaller than the non-modulated current a polarized relay'connected vin the `Zero arm of the bridge will be correspondingly operated. Asa result the circuit of the relays which serve to cutfin the resistances l5 will be acted upon andthus selection of the magnets for perforating the stripvis insured.

'I'he compensating current, as previously pointed out, is preferably derived fromrthe photo cellamplierin order that an absolute zero for 20 the shade or density scale may be'obtained. But if this isdispensed with alocal source of supply may be employed. i

Fig`.1 shows anernbodiment of the invention by way of example 'for an arrangement adapted 25 to convert l5 density values. In order that a subdivison of a density scale containing 15 gradations bythe' dual' system may be obtainedthe four elements l, 2, d, and 8 are required, in other words, i fundamentally speaking, the four-unit 30 code will be suiiicient.V With the said elements it is feasible to represent all 'of the values between 1and15.' i

'I'he photo-cell amplier `Viurnishes the carrier frequency ,fi andthe modulated carrier and 35 sidebands f2. These frequencies are separated by the filters f1, f2 where f1 is simply a Very sharply tuned resonant circuit soy as to select only the carrier frequency, whereas f2 is a band-pass filter whose mid-frequency coincides with the carrier 40 frequency and whose band width is wide enough to pass `all the generated side-bands. The output of the ilter f2 is fed to the full wave rectier G2. The output of the filter ji is fed to a rectier Gi through' an automatically variable at- 45 tenuator. The outputs of the two rectifiers Gi and G2 are then compared in a circuit which includes the vacuum tube E; The voltage fed to the rectifier Gi will'depend on the armature positions of the relays A, B, C, D. If these arma- 50 tures are in the position I, it will be observed that the output of fi is short circuited. It is only when the armatures are in position II that voltage will be fed to this rectifier.

To illustrate the operation of this invention, 55

ture r in position I. Cam n1 then closes to operate the relay A to pull its armature cainto position II. With the relay in this position, a voltage of density value 8 is suppliedto therectifier Gi because the resistor Ra is now-placedl in the cirl5 cuit. Since the value of the-output of theirectiA fierGi is still lessrthan the output of therectifier G2, the tube E still has its grid-.held atta negativer potential, so that the armature 1' is stillheld in v g position I. The'cam n2 then closes, but inasmuch f 20 as the armature 1 is held in position I, the polar``Y vity'of the battery issuch as tokeep thearrnature;

a. in positionII. Cam n3 then closesand four morefunits ofvoltage are added tothe rectifier G1. .The sum of the voltages now acting on the.- 25 rectifier G1. is 12, which is greater thantheden-- sity valueV ll, and so vthe grid of theftube Eis made positive.` This permits currerntvto. ow through the relayl'tV topull the armature r toVV position II. *Cam` m their closes and the polarity of the bat-- 30 tery is nowL such as to pulltherarmature b back to position I. Thisshorts out the resistance R4.V Camus then closes the armature ns and the sum; of'thevoltages acting. on the rectifier isjnow 10 units. This makes the grid of tube Enegative so that therelay R. operates to pull the armature- 1 to position I. Cam ma thencloses, but the polarity of the-'current owing through the relay 'coilsof C continues to hold the'armature c in .po-

sition II. Cam 1m then closes armature m' and adds another unit of voltage tofgivecomplete; balance. The closureY of the armature 11s con.- tinues'to hold thefarmatured in position II; In. this condition then the voltage of.r the-unmodu lated frequency is equal toY that of the modulated frequency. Cam mi then operates to close armature 11,9 and the-perforating. magnets'MnMzand Ms receive current through the connections of the:` armatures a., c, d, which arein-:positoniIL Y YThe'perforating magnet M4 is unaffected since: i the-armature b is -infsuch afposition that itidoesV 'not' complete the circuitback' to 'the actuating: voltage. VCam ma then operatesgto` closegarmaz ture-mo which immediately restores allt'hearmatures a; 12g-c, and d back'to position Ifandllthe density` value.

. Havingv now described my invention; what VI ergy, Vmodulating the developedscarrier wave inY accordancewith' the developed picture signal. en-

. ergy, comparing thefdev'eloped carrier and the modulated carrier energies. with each other, al-

tering the resistancercharacteristic of an elecprocess is then ready to berepeatedf for the nent'.

Y1. In a picture telegraph apparatus whereinV Vrier wave energy, developing picture signal ent-- trical circuit in accordance with the difference between the compared energies and perforating a record member in accordance with the altered resistance characteristic of the electrical circuit.

2. In a picture telegraph apparatus wherein picture signals are to be transmitted as a periorated"'record,` themetl'ioduof preparing the recaltering for 'each'comparison the resistance characteristio of an electrical circuit in accordance with the electrical difference produced by the comparison, and perforating a record member in accordance with the altered resistance characteristic of `Athe electrical circuit.

- `3. Ir-rfpicture telegraphapparatuswherein picture signals: are transmittediroms` aA perforated. tape, thecombination which comprises yafplurality: ofrelays, means for producingpicture modulated photoelectric currents; meansior. producing nomv modulated.photoelectricrcurrentm meansfor corni.- paring. the modulated: current With-the nonemodulated` current; ai plurality`v of resistance. ele-'1 ments sub-divided according.` to the powers-.ofi 2 associated with` the relays, said .relaysserving to: control the resistance elements, al polarized; relayZ operated` in accordance with thefcomparison of" the two photoelectric:currents, means. controlled.

by the polarized relay-,toccause thei plurality of` relaysto cut-in circuit or `short. circuitthe'indi- .vidual resistance elements, andV perforatingl mag nets controlled in accordance with the fresistance values-cutein circuitand' shorticircuited.tozcontrol theperforations representative.- of.: the' picture subject upon the message tape.;

4'. In fpicture telegraphapparatus wherein picture signals are. tr'ansmiiitedz from'ia perforated tape, the combination which comprises; aplurality off: relays, means.'I for." producing picturea modulatedfphotoelectric currents, means for pro ducing lnon-modulated photoelectric i currents; a

bridge; circuit for-comparing thefmodulated. cur.- f Y rent with the non-modulated 'current',-.a plurality of resistanceV elements: subdivided according.. to powers of two associated. with the relays;v said: relays serving toicontrol theeresistancerelements;v a polarizedfrelay operatedginpaccordance.- with a comparison of.V the two'photoelectric currents', rneanszcontrolled by the polarized relay' to causethe pluralityfof .relaysto cut-n circuit or shorty circuit the individual resistance elements, and perforating magnets controlled" in' accordance with the resistance values cut-in circuit and short? circuited. to. control. the Vperforations representative-.ofthe picture subject uponthefmessage tape.

5. The-`v system claimed inf'claim 31 comprisingV in addition alocal circuitfor.energizing'theper foratinge' magnets.

6. The system claimedin claim 3v comprising in' addition cam contacts for controlling thefoperation of the conversion relays and perforatormagnets; l

JOHANNES HERRMANN. 

